Apparatus for applying thermoplastic fluids are frequently also referred to as application heads and are used, for example, when substrates in film form or layer form are to be coated with fluid adhesive, for example, hot melt adhesive, over a surface area thereof or in beads in order to produce given application patterns, for example, shapes of the applied fluid. The fluid adhesive is usually stored in a fluid source such as a melting device. That fluid source is communicated with a main body of the apparatus by way of a hose connection. The fluid adhesive is conveyed by means of a conveyor means such as for example a pump into the apparatus and further conveyed through a distributor passage and in so doing passes a valve body of an application valve. The distributor passage communicates with a nozzle opening from which the adhesive is delivered and applied to a substrate. As the substrate is movable relative to the apparatus the fluid is applied to the substrate over the surface thereof. In known apparatus of that kind the nozzle opening is typically in the form of an elongate slot. The length of the operative portion of the slot can be adjusted by a piston arranged movably in the longitudinal direction in the distributor passage. Such an apparatus is known, for example, from DE 299 08 150. Apparatus are also known with which adhesive beads or strips can be applied.
Some problems arise in operation of the known applicator apparatus. Adjustment of the width of the area of the fluid to be applied is effected by a pushing or pulling movement of a piston in the distributor passage. While a pushing movement involves fluid being urged out of the nozzle arrangement in addition to the desired application thereof, air is sucked into the nozzle arrangement when the piston is performing a pulling movement. It is to be noted that when there is air in the nozzle the nozzle has to be vented before it can be brought into operation again. It is essentially a change in volume in the interior of the distributor passage that is responsible for that adverse effect. A further disadvantage is that applicators of the above-described kind occupy a comparatively large amount of space as, in addition to the space required by the apparatus itself, there must also be sufficient space at one side of the apparatus in order to be able to accommodate the piston in the condition of maximum extension thereof. That makes it difficult, inter alia, to arrange a plurality of applicators apparatus in a row with each other at a small spacing in mutually juxtaposed relationship. In the industrial production of substrates to which a fluid is applied, that has the effect of increased manufacturing costs.
Consequently, an object of the invention is to provide an apparatus which, as substantially as possible, alleviates the disadvantages found in the state of the art and with which various application patterns can be produced in a simple fashion.